LED is a light emitting device, which is operated in forward conduction to transform the electric energy into nearly monochromic light with narrow wave length profile in visible light region by recombination of holes and electrons. An LED has lower power consumption than that of a typical lamp or glowing lamp as well as a longer life. At present, there are LEDs with various colors, which have been manufactured and can be used to show color images. Moreover, because of high brightness, stable color tone, and high switch speed faster than that of human eyes, the LEDs can display a color image with progressive change and are widely used as dynamic image display devices or to construct large display panels.
With reference to FIG. 1, a conventional LED cluster system includes a CPU 10, a plurality of module controllers 20, a plurality of drive circuit boards 30, and a plurality of LED cluster strings 40. Each LED cluster string 40 includes a plurality of LED clusters 50, each comprising various number of LEDs 60 with specific colors and an outer case 70, as shown in FIG. 2. A plurality of LEDs 60 are located on a base 80. The input signal from the drive circuit boards 30 is sent to the base 80 by conducting wires 90, and then provided to each LED 60. The other space within the outer case 70 is filled with suitable filler 92, such as epoxyresin, to form an effective insulation structure to protect the internal connected wires for long term use outdoors against damage due to sunlight and rain.
The image signal including VGA/SVGA or other format of images from RS232 or other transmission interface is received and then appropriately processed by the CPU 10. The resultant data are transmitted to module controllers 20, each controlling the corresponding drive circuit board 30. The drive circuit boards 30 are connected in series so that the first stage drive circuit board will pass the suitable signal to the next stage, and in such a manner the last stage will receive the desired signal from its previous stage. Each drive circuit board 30 is used to drive the corresponding LED cluster string 40. The LED clusters 50 in the LED cluster string 40 are generally arranged in a matrix on a plane to form a rectangular display unit, and further several such rectangular display units may construct a large LED display with a specific shape.
The above LED cluster system needs a discrete drive circuit board 30 to switch all the LEDs in the LED cluster string 40 so that the whole structure becomes complicated and occupies larger space. For a large display device, it is inconvenient that more devices are needed and repair frequency is increased to decrease the working hour and the whole system efficiency.
Therefore, an LED cluster system with easy maintenance and fewer devices as well as improved characteristics is highly desirable.